Mobile phones generally use vibration as a means for informing the user of incoming calls. The silent alert provided by vibration is helpful in instances where an alerting sound is inappropriate, or where an alerting sound is inadequate. Thus, tactile sensation is used to notify the mobile user of calls or other events, such as alarms, calendar reminders, etc.
Many mobile phones use two or more eccentric mass vibrator motors to produce a greater vibration or produce haptic effects for silent alerts. Eccentric mass vibrator motors are typically driven at a single direct current (DC) voltage to produce a sustained vibration. Internal variation in each vibrator motor may cause one motor to rotate at a different speed and rotational phase relative to another vibrator motor that is also embedded in the same mobile phone, even when driven by identical voltages. Vibrator motors that are driven at different speeds and phases may interfere or partially cancel out each other's vibrations. The net effect of their vibrations may result in a dampened or reduced vibration for the entire device. Thus, a system and technique is needed to maximize the vibrations from multiple vibrators in a single device.